The present invention is related to cut-resistant yarns and associated fabrics, cordage, or non-woven products, which may be produced with the yarn. It is also related to static dissipative materials, materials reinforced for strength, and abrasion-resistant materials. Most particularly, the present invention is related to the above products when containment of a core material is required due to the potential for hazard to the employee, product, or environment if the core material is exposed.
There has been significant activity in recent years with regard to the manufacture of yarns and fabrics for cut-resistant protective apparel. Many of these activities deal with the use of stainless steel wire in conjunction with various fibers to attain an optimal balance of cut resistance and flexibility, coupled with cost of production.
U.S. Pat. No. 4,384,449 to Byrnes, Sr., et al. teaches the use of a longitudinally positioned wire strand covered with aramid, and the numerous resulting advantages of such wrapped wire. One advantage is superior cut resistance performance, when compared to gloves formed of pure aramid. Byrnes, Sr. also describes improved knitability on a conventional glove knitting machine, and improved dexterity of a glove knitted from such a wire yarn.
U.S. Pat. No. 4,470,251 to Bettcher extends the teachings of the above-mentioned Byrnes, Sr. patent by illustrating two primary discoveries. First, that two or more smaller wire strands yield greater flexibility than one strand, while allowing a larger quantity of wire to be used, and the use of a longitudinally positioned fibrous strand incorporated with the wire strands further improves flexible movement. Second, Bettcher demonstrates that an outer covering formed of a polyamide, such as nylon, improves the comfort of the glove to the wearer.
Kolmes/Plemmons, in U.S. Pat. Nos. 4,838,017 and 4,777,789, teach the wrapping of annealed stainless steel wire about a core fiber; wrapping the strands of wire in opposing directions and further increasing flexibility of the fabric while maintaining cut protection. Kolmes/Plemmons also documented a broad range of fibers that can be used in the core and outer wraps of the composite yarn.
The established prior art referenced here offers teachings that have improved the state of protective apparel. While each is representative of improvement, the present invention extends far beyond these prior teachings and demonstrates a novel and unique approach which solves a serious and heretofore unaddressed issue related to the manufacture of protective apparel. One previously unrecognized problem is the fact that in the use of wire composite yarns, the wire strands frequently break, puncturing the skin of the wearer, contaminating various manufacturing and production operations, and exposing the wearer to the possibility of disease. Wire will invariably fracture after repeated flexure and will penetrate the surface of any known composite yarn.
The present inventor has discovered that the invention taught herein provides a method of containing wire and other materials such as fiberglass when these materials are used as the yarn core. To date, there has been no serious attempt by the Food and Drug Administration (FDA) or the U.S. Department of Agriculture (USDA) to eliminate the use of such materials as a yarn core, but the issue is volatile and will eventually need to be resolved. The resolution may not be one which industry finds acceptable or even practical.
Wire and fiberglass are known to provide additional cut resistance to composite yarns by microscopically altering the edge of the cutting surface. This is due to exceptional high density and abrasiveness, which dulls the edge of any cutting instrument or device that contacts the material. Wire and fiberglass also add strength to a yarn. The materials are preferred because of the many benefits they add to a composite relative to the cost. However, these same materials are controversial because they cannot be allowed to escape from the composite yarn into the work place for environmental and/or health reasons. The present invention provides a composite yarn and fabric which may selectively incorporate wire and/or fiberglass and/or other necessary but potentially harmful materials into the basic yarn core, but which offers protection to the worker from exposure to the materials, which materials may fragment or splinter and threaten the health of the worker and also damage the end product.
The present invention provides a novel method of forming a containment barrier around a single component or multi-component core of such controversial and potentially contaminating materials, and substantially decreases the risk of these contaminates being released. The foundation of the present invention is a composite yarn which uses melt-fusible thermoplastics or liquid adhesive coatings to encapsulate and thereby isolate one or more core materials which may present a threat of contamination to workers or the environment. This novel yarn is basically comprised of one or more core materials which are covered in thermoplastics or liquid adhesives and additional layers of material which form one or more outer layers. The combination is then heat-set or otherwise cured to form a flexible fiber barrier which surrounds and entraps the unsafe core.
In a first method of manufacture, the barrier which contains the selected core is created by melt fusing a thermoplastic material with other differing fiber products in such a way that these undesirable materials are trapped between a shroud of fused fibers and a fiber core. In other embodiments, materials which are longitudinally positioned to form the core are encapsulated in a continuous fibrous sheath with no adhesion between the sheath and an inner core yarn.
It is preferred to trap wire in a fused-fiber layer having a smooth outer surface which is unlikely to bond with subsequent outer cover layers. Because wire itself has a smooth surface unlikely to bond with thermoplastic, it is important that the core bond to the thermoplastic and isolate the wire therebetween. The combination becomes a highly effective containment vehicle that retains a high level of flexibility. While the end product, such as a glove, may become slightly more rigid after heat-treating to retain shape, the composite yarn is highly flexible and can therefore be easily knitted, woven, braided, or otherwise formed into a glove or other product. There are many different materials and processing methods available to form the composite yarn, depending on the end use desired. Conventional covering or wire-wrapping equipment is most suitable to manufacture this form of the composite yarn. Other equipment may be used as needed to preprocess materials that can later be wrapped or used as wraps. Examples are commingling machines, twisting equipment, and extruding machines.
It has also been discovered that a new group of adhesive coatings can be utilized and do not require the application of heat to fuse the containment fibers together. Most of these adhesive coatings are liquid at room temperature, enabling a method which allows greater freedom in yarn design by eliminating the effect that high temperature curing can have on fibers. With the exception of those compounds, which become thermoplastic when cured, these adhesives are thermostable and normally will not return to their original state. Therefore it is possible to manufacture yarns containing adhesives with cured melting temperatures higher than the associated fibers.
The group of useful adhesives includes, but is not limited to polyurethanes, silicone, natural or synthetic rubber, polysulfide systems, epoxy-polysulfides, vinylidene chloride and blended polymers derived from this group. The novel method eliminates the necessity for in-line curing ovens because curing occurs within the protective outer sheath. As will be described in more detail in the following material, coatings can be applied, covered, and the yarn taken up on the finished yarn package in a space of approximately sixty inches, with the yarn being processed at speeds of 150 feet per minute or more.
Methods of application will vary somewhat depending on the materials being processed, the volume of adhesive being required, and the characteristics desired for the finished product. These methods are more fully described below.
In either method of manufacture, the basic core of the composite yarn is selected from a group of fibers or types of other materials, which may be spun, continuous, multifilament, or monofilament. The basic core is selectively comprised of a single strand or multiple strands of single fiber type or a mixture of fiber types. The core structure is virtually unlimited and may include fiberglass, wire strands, thermoplastics, and/or other such controversial materials or combinations of such materials. The core structure may be of a plurality of such fibers combined by blend spinning, twisting, extrusion or any other method deemed appropriate to accomplish the desired core and end product.
Several previously unknown benefits of yarns manufactured in accordance with these methods have been discovered. It has been found that abrasives such as wire or fiberglass perform their function better when locked firmly in place. The function of abrasives in cut resistant yarns has been explained as dulling the cutting edge and thereby increasing the performance of the other high strength fibers. When wire is used, it tends to move away from the cutting edge exposing more fiber to the threat. When wire is fused in place as with the present invention, it engages the edge more directly and is more abrasive. It effectively shields subsequent layers until the full abrasive effect is used. This is also true with fiberglass. Fiberglass is not effective once it is fragmented and this occurs quickly upon contact with the cutting edge and during normal flexure.
By bonding the glass with the methods described, it is less easily shattered. The maximum abrasive ability is obtained by presenting the glass as a unified and unmoving abrasive surface that is not easily shattered. By making these abrasives more effective, it is now possible to attain equal cut protection with a lower abrasive content or to increase protection with equal contents.
When the cutting threat is from a chopping blow as opposed to a slashing movement, the present invention also exhibits unique abilities. The fused fibers of the invention are pulled in the direction of the cutting edge thus increasing the concentration of protective fiber and abrasives in the threat area. This increases the level of protection to this type of threat.
It has also been found that this method of manufacturing creates a yarn with improved abilities to absorb impacts and vibration of all types. This is due to the resilient properties present in the compounds used for fusing the composite together. This characteristic is useful to dampen vibration and provide a measure of protection from blunt trauma.
The core containment barrier has been found more useful in containing wire than originally believed. It was believed that longitudinally positioned strands of wire should not exceed 0.002 inch diameter due to an increased likelihood of puncturing the core containment barrier. Success was found with longitudinal wire strands of 0.006 inch diameter without increasing the overall diameter to the finished yarn. This allows the use of heavier wire strands with minimal risk of barrier puncture.
Finally, it has been observed that embodiments having cores formed largely of melt fusible thermoplastics become hollow after heat treatment. These embodiments are very unique and exhibit improved ductility. This is important in apparel applications where wearer comfort is important.
In some embodiments, rather than bond the core directly to the thermoplastic adhesive, it is desirable that the selected core is next covered with a layer of material which creates an inner core containment barrier separating the core from the surrounding melt-fusible thermoplastics. This is necessary to prevent the core structure from bonding with the thermoplastics and thereby restricting flexibility. Core materials that are particularly brittle will deteriorate quickly if not allowed to move freely within such a shroud. This inner core containment barrier may be of any material that has a higher melt point than the thermoplastics that surround it.
Using the heat-set method rather than liquid internal coating, a preferred embodiment includes a basic core, and around the circumference of the basic core, the first layer of one or more strands of wire may be wrapped to provide a second component to the core. The wire may be wrapped in one direction with one or more strands applied parallel to each other, or the wire may be twisted or combined in any other known way. The wire may also be wrapped in opposing directions relative to each other, with one strand being clockwise, and the other counterclockwise. The preferred wire is an annealed stainless steel 304 with a range of 0.008 inch diameter or smaller. The most preferred is 0.0045 inch for a single wrap, or 0.003 inch for a double wrap. Finer strands may be used when there is a combined plurality of wire strands. In such embodiments, using wire of 0.002 inch diameter or more, wrapping is preferred. The wire wrapped about the basic core may be wrapped at a pitch of 1 to 100 turns per inch, as the embodiment requires. It has been observed that the helical shape that is thus formed directs the wire's angle more to the center of the composite yarn structure. This becomes important when a wire strand fractures. Longitudinally positioned wire strands tend to project a rigid point when broken. This rigid point is then so oriented as to puncture the surface when the yarn is flexed and is difficult to contain.
Following application of the wire component to the basic core and/or the inner core containment barrier, an adhesive layer to be added to the composite yarn is selected from the group of melt-fusible thermoplastics. These may be polypropylene; low, high, or ultra-high-density polyethylene; low-melt nylon polyamid; or polyamid blends; or low-melt polyesters. A number of higher melt temperature thermoplastics exist which have not been tested, but are believed to be applicable for higher temperature applications and embodiments. This layer adhesive may be applied in several different ways, including wrapping, twisting or spinning about the core and the inner core containment barrier; may be longitudinally positioned with the core, extruded over the core, blended with the core, commingled with the core, or any combination of these methods. The thermoplastics also may be applied to the wire strands prior to wrapping the strands around the basic core. The selected method of combining the thermoplastics with the wire is dependent upon the number and size of the wire strands being utilized. The wire strands may be wrapped, twisted, paralleled, paralleled and wrapped with more thermoplastic, paralleled and wrapped with very fine denier non-thermoplastic, or the wire may be coated by means of any of the more conventional coating methods.
Selected thermoplastics for this layer may be monofilament, multifilament, spun or blended with other materials. The percentage of thermoplastic content in this layer is limited only to that which is necessary to properly contain and stabilize the underlying materials. When combining with the wire prior to wrapping the wire around the basic core member, two benefits are attained. First, prior combining allows a step to be eliminated in processing by not requiring a separate wrapping of thermoplastic. Secondly, the thermoplastic is concentrated only in the area that surrounds the wire, leaving some unfused areas to increase the flexibility of the composite. Some of the more effective methods will be detailed below.
The next layer is the primary core containment barrier and is selected from a broad group of synthetic or organic materials including but not limited to: polyester, nylon, aramid, high density polyethylene, ultra high molecular weight extended chain polyethylene, such as Allied Signal's SPECTRA, cotton, wool, polycotton, rayon, Hoechst Celanese's PBI, Dupont's TEFLON and blends thereof. The exceptions are those materials which are the same as those to be contained, and materials having melt points which are lower than the selected thermoplastic. This layer serves several functions:
1) It forms the layer of fiber that is fused with the underlying adhesive layer to form a shroud.
In certain embodiments wrapped wire is the material to be contained and this layer is utilized to fuse with the material of the basic core around which the wire is wrapped. This results in a sandwich effect that thoroughly traps the wire in a flexible capsule or fused fibrous material that is almost impenetrable.
2) In embodiments using wrapped wire, this shroud functions to prevent the wire from moving as the composite is heated. The selected fiber must therefore be of reasonably high tenacity and not generally susceptible to loss of strength at the fusion temperature of the underlying thermoplastic.
3) This layer adds cut resistance to the finished composite yarn.
4) This layer serves as a shroud that has sufficient thickness to absorb the underlying melt-fusible polymer and prevent the polymer from passing to the outer wraps. This is of particular importance when subsequent outer covers must be able to function independently of the core and core containment barrier yarns. Independent movement is sometimes necessary primarily for flexibility, but also allows the performance characteristics of the yarn not to be impeded by entrapment. It has been observed that yarns are more cut and/or abrasion resistant when the yarns are allowed to move freely with the cutting or abrading surface. This is simply illustrated by observing the relative ease with which a yarn may be cut under tension, versus one that is cut under less tension.
In addition to the above functions, when used in the wrapped wire embodiments, it is preferred that this third layer be wrapped at the number of turns per inch which provides an angle as close to 90 degrees relative to the wire as feasible. Near perpendicular angles are optimal to allow the finished composite yarn to perform. Present embodiments have attained a 70 degree angle at 8 turns per inch using 840 denier nylon. In other embodiments it is necessary to apply a lighter denier at a very high range of turns per inch. This is particularly true where multiple ends of wire are wrapped in opposing directions. The turns per inch must be a combination of optimal angles, total encapsulation, density of the layer and the fiber's ability to prevent movement of the wire during the heat cycle. It should be noted that the type 304 alloy of stainless steel has a coefficient of thermal expansion equal to 10.1.times.10.sup.-6 per degree rise in temperature Fahrenheit. If the composite is processed at 295 degrees Fahrenheit then a one-inch section would normally expand to 1.00226846 inch. While this amount of movement may appear small, it does have the ability to deform the fabric if not controlled. Testing has shown that wire can push through the thermoplastic layer as the wire expands during the heat cycle, and this movement prevents a proper bond from forming because the thermoplastics tend to cool more quickly than wire. This layer ideally should be wrapped with a comparable range of turns per inch as the underlying core using a yarn of sufficient weight or diameter to provide complete coverage and density. However, yarns from 20 to 4800 denier may be used and may be applied from 3 to 200 turns per inch as the embodiment requires. This shroud layer may be one or more wraps in similar or opposing directions relative to one another. As with the basic core, this layer can be made up of a multiplicity of yarns, depending on the desired end effect or product.
In the preferred embodiments described below, it will be obvious that the simpler methods and yarn combinations achieve the best results.
A final, or outer, layer may also be added. This outer layer is of particular importance when the underlying layer is not capable of absorbing the molten thermoplastic and preventing it from rising to the surface of the finish product (known as "wet out"). The fiber content of this outer layer may be selected from the same group as the wire-containment barrier. There may be one or more of these outer layers and each may be similar or dissimilar. The selected material wrap may be of a single strand, multiple strands of a single yarn or a multiplicity of differing yarn fibers or types. This outer layer may also be spun over the underlying layers as with friction spinning equipment.
With use of such overlying multiple layers it is preferred, but not required, that each of the layers be wrapped in opposing directions. This method of wrapping in opposing directions is known as counterbalancing and has the effect of making the yarn balanced, straight, and with separate covering layers that tend to lock together and do not easily fray.
The combined selection of yarn fibers and types is based primarily on the end use of the yarn, the fabric or the product. Some of the more common materials are nylon, polyester, aramid, extended chain polyethylene, rayon, cotton or wool. However, the fibers/types may be selected from any of the synthetic or natural materials group. Any one of the layers or wraps may serve any of the functions of enhanced cut resistance, abrasion resistance, improved comfort to the wearer, increased thermal performance, enhanced texture for handling special materials, improved knitability, or other such characteristics.
When utilizing the liquid adhesive method of manufacture, the liquid coatings are applied to one or more of the aforedescribed core materials, prior to application of the other layer(s). This is done by drawing the selected core member through a trough mounted near the entry point of the covering mechanism. The volume of adhesive applied is controlled by dilution of the fluid, by varying the number of core yarns coated, and by altering the core's dwell time in the trough with repeated loops over a submerged feed wheel.
Following this liquid application the core member enters directly into the covering spindle(s) or spinning head and is covered with one or more fibers which absorb the excess adhesive and form the aforedescribed containment barrier. Sufficient fibers should be applied to prevent any possible fluid migration to the outer surface of the yarn. By absorbing the excess adhesive and eliminating possible migration to the outer surface of the yarn, the finished yarn can be immediately wound onto a package, before the liquid adhesive is cured. It has been proven that the volume of liquid adhesive which is applied to the core can be controlled and that a finished yarn can be accomplished with sufficient adhesive to migrate close to the yarn surface, thereby affecting texture and appearance, but without bonding the yarn to the package.
Such an application has been found beneficial in modifying yarns which have an unacceptable hand or color, but which otherwise demonstrate desirable characteristics. One example of such a yarn, manufactured by Allied Signal and sold under the trademark SPECTRA, demonstrates superior strength but is too slippery or slick for use in articles such as gloves.
It has also been discovered that with this liquid internal coating process, beneficial additives may be put into the core of the yarn. One such additive is grit which can be mixed with the liquid adhesive in sufficient volume to act as an abrasive which has the affect of dulling a cutting edge, therefore aiding in the cut resistance of the finished product. Grit of a sufficient size is also effective in inhibiting or preventing puncture by surgical needles by dulling the point of the needle, and by blocking the hollow channel of the needle. By blocking this channel, the surface area of the needle is increased and further penetration is substantially inhibited.
The finished novel composite yarn is applicable to knitting, weaving, braiding, twisting, or otherwise forming into a desired fabric or product. Once the end product is provided, the final step of thermoplastic fusion generally takes place. Treatment temperatures and exposure times will vary according to the characteristics of the thermoplastic, density of the composite and thickness of the article manufactured. With gloves, for example, a typical heat treating method would make use of a glove dotting machine which is designed for precise temperature and exposure time control. Yarns may also be heat treated on the package in a dry or wet yarn-conditioning oven.